The present invention relates to a switching system modem interface.
Digitized data, such as data produced by a personal computer, can be transmitted over the xe2x80x9cplain old telephone servicexe2x80x9d (POTS) voice-band phone network using a modem. Conventional modems use POTS compatible electrical signaling to establishes a voice-band communication channel through a POTS central office switching system to a destination modem. The originating and destination modems exchange digital data by encoding the data as voice-band signals which are transported end-to-end across the telephone network. Alternatively, digitized data can be transmitted over integrated services digital network (ISDN) lines end-to-end through digital telephone network connections to destination digital terminations, typically located with destination modems for voiceband data.
Various data-over-POTS modem modulation standards exist to provide POTS-compatible voice-band encoding of digitized data. For example, modems implementing the International Telecommunications Union (ITU) V.34 standard can support 28.8 Kilobit per second (Kbps) voice-band data transmission and modems supporting the V.90 standard can support approximately 56 Kbps in the network-to-user direction, 33.6 Kbps in the user-to-network direction. Lower rate modem or FAX protocols, such as V.17, V.21, V.22, V.22bis, V.27, V.29, V.32, or V.32bis may also be used. The maximum data communication rate between the originating and destination modems is determined by, among other things, the supported modem protocol and the end-to-end electrical interference on the communications channel between the modems.
POTS telephone signals, including those exchanged by POTS voice-band compatible modems, typically originate at POTS customer premises equipment (CPE) and are transmitted over a twisted-pair wire loop terminating at a central office POTS line card. A POTS compatible line card provides signal transmission functions such as ringing voltage, CPE power, dual-tone multi-frequency (DTMF) tone detection, and pulse-dialing detection, as well as conversion of analog POTS signals to and from digital pulse code modulation (PCM) format. Conventional POTS line cards typically interface to a central office POTS switching system (a xe2x80x9cPOTS switchxe2x80x9d). The POTS switch establishes a voice-band data connection by routing a POTS call from the originating CPE to a terminating CPE. At typical digital POTS switches, POTS voice-band signals are converted to a 64 Kbps pulse-code modulated (PCM) data stream. As with other POTS-compatible services, and regardless of the modem""s supported data rate, the voice-band frequencies produced by a modem are typically encoded as a 64 Kbps PCM data stream for routing through the telephone network. Routing of modem-originated data through a POTS switch requires POTS switch resources to be dedicated to the voice-band channel between the originating and destination modems. For example, a 64 Kbps time-division multiplexed interoffice trunk may be used to provide the voice-band channel connection to a distant central office or long distance provider switch.
In general, in one aspect, the invention features a data communication apparatus for communicating data between trunk channels and a cell-based network. The apparatus includes trunk interface circuitry, data interface circuitry, and cell segmentation circuitry. The trunk interface circuitry receives continuous bit rate call data being communicated from an originator to a recipient. The data interface circuitry is operatively coupled to the trunk interface circuitry, and is operable to receive the call data from the trunk channel and to extract an original data stream. The cell segmentation circuitry is operative to receive the original data stream from the data interface circuitry and to produce data cells.
Implementations of the invention may include one or more of the following features. The apparatus may include multiple circuit cards physically connected by a backplane interface to a backplane. Backplane interconnection circuitry may couple the cell segmentation circuitry and the backplane interface to each other for data transmission. The trunk interface circuitry may receive call data from an ISDN primary rate interface xe2x80x9cBxe2x80x9d channel. The apparatus may also include control circuitry that transmit and receive control data over an ISDN xe2x80x9cDxe2x80x9d channel. The control circuitry may determine cell routing and other header field data based on received signaling data associated with a particular xe2x80x9cBxe2x80x9d channel, and may provide the header field data to the cell segmentation circuitry for inclusion in produced data cells. Call data may be a 64 Kilobit per second pulse code modulated representation of a voiceband modem signal.
Implementations may also include trunk interface circuitry that can receive call data from multiple trunk channels. The data from each of the trunk channels may be formed into data cells each having header data associating the data cells with particular trunk channels. The cell segmentation circuitry may include channel bonding circuitry to receive original data streams from multiple trunk channels, produce a composite data stream from the collection of original data streams, and produce data cells associated with the composite data stream.
Furthermore, implementations of the invention may include data cell reassembly circuitry that can extract payload data from data cells and provide the extracted data to the trunk interface circuitry for transmission over a trunk channel. The data interface circuitry may include circuitry to insert start bits and stop bits in the second call data to delimit the second original data stream. The apparatus may include an asynchronous network interface to transmit data cells from the cell segmentation circuitry to a data cell network.
In general, in another aspect, the invention features a method of producing data cells. The method includes receiving continuous bit rate call data over a trunk channel, processing the call data to extract an original data stream that is being communicated from an originator to a recipient, segmenting the original data stream into cell payload data, and forming data cells that include the cell payload data.
Implementations of the invention may include one or more of the following features. Extracting the original data stream may include extracting segments delimited by start bits and stop bits. Call data may be received over a second trunk channel, processed to produce a second original data stream, segmented into second cell payload data, and formed into second data cells. The data cells may include header data associating data cells with their respective trunk channel. Data cells may also be received over the backplane interface. Second call data may be produced by extracting payload data from the second data cells, and the second call data may be transmitted over a trunk channel. Segmenting the original data stream may include processing by cell segmentation circuitry to produce data cells that include header and payload data in accordance with the ATM Adaptation Layer-5 protocol.
In general, in another aspect, the invention features a data communication apparatus for communicating data between trunk channels and a cell-based network. The apparatus includes trunk interface means for receiving call data over a trunk channel, data interface means for receiving the call data and extracting a data stream, and cell segmentation means for receiving the data stream and producing data cells.
Implementations of the invention may provide one or more of the following advantages. The use of POTS and ISDN phone network and trunk resources can be reduced. Efficient transmission of bursty data from a continuous bit rate data source can be achieved. Other features and advantages will become clear from the description and claims that follow.